Renée Zellweger skipped the star treatment and surreptitiously slipped into the Hamptons International Film Festival premiere of “The Descendants” over the weekend as a paying customer. While stars including Susan Sarandon, Matthew Broderick and Christie Brinkley paraded down the red carpet at East Hampton’s Guild Hall, spies saw Zellweger enter the theater, dressed down, with three pals. Turns out the Oscar-winner bought tickets earlier in the day.